One Frequency In, Three Out
The story behind The Emission
Inspired by Resonance fluorescence on Wikipedia
Built with Three.js · InstancedMesh · ShaderMaterial · EffectComposer (UnrealBloomPass)
Techniques Rabi Oscillation Model · Chromatic Aberration · Bloom
Direction Build a quantum optics sandbox where cursor velocity crosses the Mollow triplet threshold and one frequency of light splits into three
Result A field of 2,500 atoms that scatter blue light under gentle movement but erupt into amber-violet-cyan triplets when driven hard enough
The Story
In 1969, a theoretical physicist named B.R. Mollow worked out what happens when you drive a single atom with a laser tuned exactly to its resonance frequency. At low power, the atom does what you’d expect: it absorbs a photon and re-emits one at the same frequency. Elastic scattering. One color in, one color out.
But Mollow’s equations predicted something strange at high power. Push the laser intensity past a threshold and the emitted light splits into three peaks — a central peak at the laser frequency and two sidebands offset symmetrically above and below. The atom creates frequencies that aren’t in the input. One color in, three out.
It took eight years for the experiment to catch up. In 1977, Kimble, Dagenais, and Mandel at the University of Rochester observed the Mollow triplet directly, along with another prediction: photon antibunching. The emitted photons refused to arrive in pairs. After each emission, the atom needed a refractory period — a minimum time before it could emit again. The light wasn’t random. It was ordered.
The transition from one peak to three isn’t gradual. Below a critical drive strength, the spectrum is a single line. Above it, three lines appear. The threshold IS the transition from classical to quantum behavior. We wanted to make you feel that threshold with your cursor.
The Take
2,500 atoms sit in a field. They’re visible: a grid of dim blue points, breathing slowly. Your cursor is the laser. Move it and the nearest atoms light up blue — elastic scattering. One frequency in, one out. The interaction is gentle, proportional, classical.
Move fast and the response changes. The drive strength crosses a threshold and each atom’s single glow splits into three: a blue-white center, a warm amber lower sideband, and a vivid violet upper sideband. The colors are not decorative — they represent the three peaks of the Mollow triplet, the spectral signature of a strongly driven two-level system.
The system rewards violence. Gentle cursor movement produces nothing but blue. Only aggressive, fast movement crosses the threshold that creates the new colors. Amber and violet don’t exist in the input. They are created by the interaction itself.
The Tech
The 2,500 atoms are rendered as a single Three.js InstancedMesh — one draw call for the entire field. Each atom is a PlaneGeometry quad with a custom ShaderMaterial. Per-atom state (excitation, drive strength, Rabi phase, refractory timer) lives in a Float32Array uploaded as an InstancedBufferAttribute, updated CPU-side every frame.
Drive model. The cursor’s position and velocity drive the atoms. A proximity falloff (inverse 1.5-power within 3.5 world units) multiplied by velocity factor determines the target drive strength for each atom. Drive ramps up fast (35% per frame toward target) and decays slowly (5% per frame), so atoms stay lit behind a fast-moving cursor like a comet trail.
Rabi oscillation. Each atom’s excitation oscillates sinusoidally as a function of its accumulated Rabi phase. The oscillation frequency is proportional to drive strength — strongly driven atoms pulse faster. This creates the characteristic population inversion oscillation of the dressed-state picture: the atom pendulums between ground and excited states.
The fragment shader branches on the drive threshold. Below 0.3, the shader renders a single circle with color interpolated from dormant blue-grey to elastic scattering blue. Above 0.3, it renders three circles: center, lower sideband (offset along a random per-atom angle), and upper sideband (offset opposite). The split distance increases with smoothstep(0.3, 0.5, drive), so the three peaks emerge gradually as drive crosses the threshold. The sidebands are intentionally brighter than the center — physically incorrect (the Mollow triplet has a 1:2:1 intensity ratio), but visually necessary so the amber and violet read against the blue.
Antibunching is modeled as a refractory timer. When excitation exceeds 0.8, the atom enters a 0.12-second dim period (15% brightness), simulating the dead time after photon emission. The effect creates micro-blinks across strongly driven atoms — the field flickers rather than glowing steadily.
Cascades fire when 8 or more atoms simultaneously exceed 0.6 drive strength. An expanding ring propagates outward, boosting the drive of atoms it passes through — a superradiance analogy where collective excitation triggers correlated emission.
Detuning drifts as a slow sine wave (25-second period), modulating the effective drive strength. A subtle indicator bar appears after 15 seconds of interaction, showing the current detuning offset.
Post-processing: UnrealBloomPass at moderate strength (0.6, radius 0.4, threshold 0.3) provides glow without washing out the triplet colors. ChromaticAberration adds subtle color fringing that increases during cascades.
The Experience
A field of blue points. Breathing. Still. You move your cursor and the nearest atoms light up — scattered blue light trails behind you like fireflies waking. Everything is monochrome. One color. Classical.
Move faster. Something changes. The atoms nearest your cursor aren’t just blue anymore. You see amber. Violet. Three distinct colors splitting from what was one. The threshold has been crossed. You’re not scattering light anymore — you’re creating frequencies that didn’t exist.
Whip the cursor across the field and it erupts. Trails of triple-colored atoms streak behind you. An expanding ring pulses outward from the hotspot, lighting up atoms in its wake. The colors are vivid: warm orange-amber, electric violet, cool blue-white. One frequency in, three out.
Stop moving. The atoms decay back to blue. Back to dormant. The new colors exist only under violence. The system punishes gentleness with monotony and rewards aggression with creation. It’s not how you expect beauty to work. But it’s how the physics works.
This blog post was AI generated with Claude Code. Authored by Artificial Noodles.